The present invention relates to radio receiver circuitry.
In communications systems, the receiver circuit employing Intermediate Frequency Band-Pass Filtering is known to have temperature dependent centre frequency characteristics. The temperature of the intermediate frequency band-pass filter (IF BPF) increases while the communications system is in use, and causes a shift of the centre frequency of the IF BPF. Generally, the temperature dependence is stronger for cheaper filters and/or filters with smaller dimensions.
Under normal conditions, the bandwidth of an IF BPF is chosen slightly larger than the bandwidth of a selected signal (i.e., a signal in a specific selected channel) to separate only that signal (or: channel) from other signals, present in the medium. For example: in the 5 GHz ISM (Industrial, Scientific and Medical) band for wireless communications, the signal bandwidth for OFDM (Orthogonal Frequency Division Multiplexing modulation) is typically 16.6 MHz, the IF BPF has a bandwidth of 18 MHz, and the separation of the centre frequencies of adjacent transmission channels is 20 MHz.
If the centre frequency of the IF BPF changes due to a change of temperature of the filter, the selected signal may be cut-off at one of the bandwidth boundaries of the intermediate frequency band-pass filter, which may cause a loss of signal strength. Also, since transmission channels are closely spaced to each other, a signal in an adjacent channel may enter into the bandwidth of the IF BPF and may distort the selected signal in the signal processing steps after passing the IF BPF.
Disadvantageously, these operational changes of the IF BPF result in a condition where the received selected signal cannot be processed reliably anymore, causing the communications system to fail its specifications due to, e.g., a high Bit Error Rate, or a low reception sensitivity.
It is an object of the present invention to provide an electronic circuit comprising an intermediate frequency band-pass filter, which compensates for the shift of the centre frequency of such a filter, due to a change in temperature.
The present invention relates to an electronic circuit having a controller arranged to receive data indicative of a shift of the intrinsic centre frequency due to a temperature change of the band-pass filter from the predetermined working temperature and to control the first selection frequency of the local oscillator for changing the intermediate frequency of the intermediate signal to follow the shift of the intrinsic centre frequency.
Thus, the present invention provides an electronic circuit which processes a selected signal reliably, irrespective of the operating temperature of the band-pass filter.
Moreover, the present invention allows the use of a standard band-pass filter without the need for a more expensive band-pass filter with less temperature-dependent properties.
Also, the present invention relates to a method to be carried out by a controller. The method carried out by the controller includes the steps of:
receiving data indicative of a shift of the intrinsic centre frequency due to a temperature deviation of the band-pass filter from the predetermined working temperature, and
controlling the first selection frequency of the local oscillator for changing the intermediate frequency of the intermediate signal to follow the shift of the intrinsic centre frequency.